Since it adds to portability and reduces the overall bulk of the wire transmission system, applicant has created a compact and lightweight wire drive mechanism. In the past, one of the most common welding wire drive systems has involved the use of aligned rollers in which the roller surfaces are knurled or roughened and coact to drive against the wire. Such knurled driving rolls roughen the surface of the welding wire thereby increasing the sliding resistance between such wire and its surrounding conduit, increasing the necessary wire driving force and also wearing the various conduit surfaces and welding gun tips with which such wire comes into contact. To avoid such knurled wire driving rolls, applicant utilizes a pair of planetary driving rolls incorporated in a rotating drive head for imparting linear or linear-like motion to the welding wire. As shown in the following patents, welding wire drive systems utilizing planetary type rollers are known to be old prior to applicant's invention:
U.S. Pat. No. 3,014,519--Wright, PA1 U.S. Pat. No. 3,684,152--Boden, PA1 U.S. Pat. No. 3,738,555--Karnes et al., PA1 U.S. Pat. No. 4,049,172--Samokovliski et al., PA1 U.S. Pat. No. 4,098,445--Samokovliski et al.
In common, such planetary drive heads include a plurality of rollers having axes of rotation skewed to each other and laterally offset from the axis or line of movement of the wire being driven. When the roller axes planetate about the wire, the roller peripheries engage the wire and create a threading-type action causing the wire to move generally linearly as the head rotates. The direction of wire movement can be reversed by reversing the rotative direction of the head.
Most of the prior art planetary roller drive mechanisms, while avoiding the use of knurled driving rollers, have been primarily concerned with the means for adjusting the position of the rollers to accommodate different size wires and for compensating for centrifugal forcing tending to move the rollers out of driving engagement with the wire. Applicant is also able to accommodate various size wires through the use of means for manually adjusting the radial position of such rollers relative to the wire to be driven. However, applicant's departure from the prior art wire drive mechanisms is in the recognition of the desirability of inducing a vibration into the wire being driven and providing a wire support system which allows such vibration to be perpetuated through the system and up to the point of use of such wire as at a welding gun tip. Particularly as applied to feeding welding wire, vibrating such wire has several advantages. First, by introducing a vibration to the wire tip at the welding gun a stirring of the weld puddle is achieved which helps eliminate undesirably included materials, such as oxides, from the weld joint thereby improving the weld quality. Next, the wire vibration reduces the frictional drag or resistance between the wire and the conduit through which it is being driven. By reducing wire/conduit friction, the tendency of the wire to collapse or bird-nest under wire driving forces is reduced thereby increasing the distance the wire drive mechanism may be located from a workpiece or increasing the distance over which said wire may be driven.